Radiation detector

ABSTRACT

The present invention provides a radiation detector capable of detecting the radioactive substance accumulated in the tissue inside a body by inserting a detection unit into blood vessels. In the radiation detector of the present invention, comprising a detection unit ( 2 ) having a bar-type scintillator ( 4 ) which emits light by an incidence of radiation so as to transmit the light from the scintillator through an optical fiber, the detection unit is formed in a size capable of being inserted into the tubules while fine convexoconcaves are provided on the peripheral surface of the scintillator.

TECHNICAL FIELD

The present invention relates to a radiation detector for detectingradiation leakage in tubules and radiation substances present in tissuesin the body system. More specifically, it relates to a radiationdetector for detecting radiation substances accumulated in the tissuesin the body system by inserting a detection unit into a blood vessel ofcoronary artery and the like after administering a radiopharmaceuticalinto the body system.

BACKGROUND ART

In the followings, the present invention will be described by referringmostly to its application inside blood vessels. Heart diseases amongJapanese has been increasing year after year and it has now grown to bein the second place for the cause of death. Especially, unstable anginapectoris, acute myocardialinfarction, and inschemic heart sudden deathare called as acute coronary syndromes, which are very serious diseases.Most of acute coronary syndromes are caused by thrombus formationtriggered by a rupture of plaque of coronary artery.

Conventionally, invascular lesions including acute coronary syndromesare examined by nuclear medicine method. Nuclear medicine method isperformed by utilizing radiopharmaceuticals accumulated in the subjectpart of the body, which have been administered beforehand. Diagnoses arecarried out by detecting the radiation emitted from theradiopharmaceuticals accumulated in the target area by a detectorgenerally placed outside the body and forming an image based thereon.Although the nuclear medical detection is inferior to CT and MRI as amorphologic diagnosis means, it is superior as a description diagnosismeans for functions and tissue of living bodies. Therefore, it has beenwidely used in clinical examinations. On the other hand, nuclearmedicine method devices have been proposed, in which a detector isinserted inside a human body for special purposes. However, these typesexhibit a low sensitivity so that they are not used for actualdiagnoses. Detectors which can be inserted to narrow blood vessels suchas coronary arteries have not been developed so far.

The nuclear medicine method device for performing examinations byplacing a detector outside the human body, and the nuclear medicinemethod device for performing examinations by inserting a detector insidethe human body will be described in detail. The former nuclear medicinemethod device for performing an examination by placing the detectoroutside the body comprises a detector (in general, a gamma camera)outside the body for detecting the radiation emitted from theradiopharmaceutical administered beforehand and a computer for formingan image based on detected signals. The detector comprises ascintillator and some ten photomultipliers provided inside. Emission oflight is caused upon incidence of the radiation to the scintillatoremitted from inside the body and the light signals are transmitted tothe photomultipliers corresponding to the positions to be converted toelectric signals. The signals are formed into images by a computer to beused for diagnoses.

In this nuclear medicine method device, the detector is placed outsidethe body so that there is a distance between the detector and the targetbody part. Thus the radiation is scattered and attenuated by thedistance and the living body tissue present in between, thereby causingdeterioration of the resolution. Also, when the target is the one thatis moving such as the heart, deterioration of the resolution cannot beavoided. The maximum resolution is about 5 mm. Therefore, it isimpossible to discriminate a very small accumulation of the radiation inthe case of, for example, lesions inside the coronary arteries fromother radiations. Further, the device is on a large-scale, so that it isvery hard to be used in emergency cases such as in a room for the heartcatheter where acute coronary syndromes are treated.

There are nuclear medicine method devices in which the detector isminiaturized to be inserted inside the body for a special purpose.However, they are not used practically. As an example of this type ofthe device, U.S. Pat. No. 4,595,014 discloses an intracavity radiationdetector. A collimator formed by a substance such as tungsten is mountedonto the device for obtaining the directivity of the radiation enteringinto the scintillator. In this case, it is necessary to thicken thecollimator especially for the radiation with high energy in order toincrease the directivity of the incoming radiation. The volume of thescintillator is reduced and the sensitivity is deteriorated as thethickness of the collimator is increased. Also, the detector of theabove-described detection device cannot be inserted into narrow vesselsof the living bodies.

As another example of the device in which the detector is insertedinside the body for performing an examination, Japanese PatentUnexamined Publication No. 5-11055 and Japanese Patent UnexaminedPublication No. 8-94760 disclose luminal radiation detectors. In thesedevices, two scintillators with the diameter of about 8 mm are arrangedin parallel or in vertical and optical fibers are connected to eachscintillator for guiding the light signals to two photomultipliers so asto detect only the coincident signals. Thereby, background is reducedand, at the same time, the directivity of the incoming radiation isobtained. In this method, different light signals by the radiationsemitted from different scintillators are coincided so that thebackground can be reduced. However, the sensitivity for γ-ray becomeslow since it is very rare that one photon such as γ-ray makes bothscintillator emit the light. Therefore, it is impossible with the methodto miniaturize the scintillator to be able to be inserted into the bloodvessels.

DISCLOSURE OF THE INVENTION

The present invention has been designed to overcome the forgoingproblems. The object of the present invention is to provide a radiationdetector which is capable of detecting a radiation leakage of tubules ora radiation substance accumulated in tissue inside a body by inserting adetection unit into the tubules or inside the blood vessels.

In order to achieve the foregoing object, the present invention providesa radiation detector for detecting a radioactive substance present in atubule, comprising a detection unit having a bar-type scintillator whichemits light by an incidence of radiation so as to transmit the lightfrom the scintillator through an optical fiber, wherein the detectionunit is formed in a size capable of being inserted into the tubule whilefine convexoconcaves are provided on the peripheral surface of thescintillator.

The present invention provides a radiation detector for detecting aradioactive substance present in tissue in a body system, comprising adetection unit having a bar-type scintillator which emits light by anincidence of radiation so as to transmit the light from the scintillatorthrough an optical fiber, wherein the detection unit is formed in a sizecapable of being inserted into a blood vessel while fine convexoconcavesare provided on the peripheral surface of the scintillator.

In the radiation detector, the sensitivity is deteriorated as the sizeof the scintillator is reduced. When the radiation goes through thescintillator, there is no emission of light generated. In other words,there is more possibility of the radiation going through thescintillator as the scintillator becomes smaller and the sensitivitybecomes deteriorated. In the radiation detector of the presentinvention, while miniaturizing the scintillator to be able to beinserted into blood vessels, fine convexoconcaves are formed on theperipheral surface for suppressing the sensitivity deterioration due tothe reduction of the size. Thereby the reflection of light emitted frominside the scintillator is diffused on the surface of the scintillatorto be effectively guided to the optical fiber.

In the present invention, the detection unit is formed in a size capableof being inserted into tubules for detecting the radiation leakage orinto blood vessels for examining the presence of lesions. Generally, itis formed in a size which can be inserted into coronary arteries.Specifically, it is desirable that the diameter (thickness) of thescintillator be 1.5 mm or less.

In the present invention, the shape and the like of the fineconvexoconcaves are not specifically limited as long as it is capable ofdiffusing the reflection of light emitted from the inside thescintillator on the surface of the scintillator. Also, theabove-described convexoconcaves may be formed in a part of theperipheral surface of the scintillator or on the whole surface. However,it is appropriate to provide them on the whole surface in considerationof improving the sensitivity. There is no limit to the means for formingconvexoconcaves on the peripheral surface. However, as an example, theperipheral surface may be polished using, for example, sandpapers.

The radiation detector of the present invention may further comprise thefollowing structures as will be described in the embodiments describedlater.

-   {circle around (1)} A structure in which a part of the top end face    and the peripheral surface of the scintillator is covered by a    radiopaque substance.-   {circle around (2)} A structure in which a rotary moving device is    provided for rotating and moving the detection unit back and forth    in a tubule or inside a blood vessel.-   {circle around (3)} A structure in which, as the optical fiber for    transmitting the light from the scintillator, an optical fiber    aggregation which is obtained by bundling up thin optical fibers to    have substantially the same diameter as that of the scintillator is    used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the overall structure of an embodimentof a radiation detector according to the present invention;

FIG. 2 is an enlarged view of a detection unit in the radiationdetector;

FIG. 3 is an enlarged perspective view of a scintillator of thedetection unit;

FIG. 4 is a schematic view showing the structures of the rotary movingdevice and the instrument of the radiation detector;

FIGS. 5A to 5C, and 5F to 5H are spectral diagrams showing the pulseheight spectra of photomultipliers, respectively;

FIGS. 6D, 6E, 6I, and 6J are spectral diagrams showing the pulse heightspectra of photomultipliers, respectively;

FIG. 7 is a graph showing the maximum wave of the photomultipliers;

FIG. 8 is a graph showing the result of the detecting property obtainedby the sensitivity test of the radiation detector shown in EXAMPLE 2;

FIG. 9 is a graph showing the test result of the detection scanningobtained by the sensitivity test using simulated blood vessels; and

FIG. 10 is a graph showing the linearity of the counting values for theradiation source concentration gradient examined in the sensitivitytest.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described by referring toaccompanying drawings. However, the present invention is not limited tothe embodiments described below. FIG. 1 is a block diagram showing theoverall structure of an embodiment of a radiation detector according tothe present invention and FIG. 2 is an enlarged view of a detection unitin the radiation detector. FIG. 3 is an enlarged perspective view of ascintillator of the detection unit and FIG. 4 is a schematic viewshowing the structures of the rotary moving device and the instrumentsof the radiation detector.

In the radiation detector of the embodiment, numeral 2 is a detectionunit, 4 is a column-shape scintillator provided in the detection unit, 6is a radiopaque substance covering a part (almost a half) of the top endface and the peripheral surface of the scintillator 4, 8 is acylindrical X-ray opaque substance mounted onto the top end part of thescintillator, 10 is an optical fiber aggregation connected to the rearend part of the scintillator 4, 12 and 14 are two optical fiberbranches, 16 is a tube-type lightproof cover for covering thescintillator, the optical fiber aggregation, the optical fiber branchesand the like.

The above-described scintillator 4 is formed of plastic scintillatorwith the diameter of about 1.00 mm and the length of 5.00 mm, cesiumiodide, BGO, YAP (Ce) and the like, and fine convexoconcaves are formedon the peripheral surface. The above-described optical fiber aggregation10 is formed by bundling up a number of optical fibers of about 20 μm indiameter to have almost the same diameter as that of the scintillator 4.Examples of beta-ray or gamma-ray opaque substance 6 are tungsten,tantalum, gold, silver and the like. Examples of the X-ray opaquesubstance are tungsten, tantalum, copper alloy, stainless steel and thelike and examples of the materials for the lightproof cover 16 arestainless steel, lightshield plastic and the like.

Further, in the radiation detector of the embodiment, numeral 18 is arotary moving device, 20 is a controller and 22 is a computer. Therotary moving device 18 is for rotating and moving the detection unit 2both at a constant speed inside the blood vessel. An instrument 24 isenclosed inside the rotary moving device 18 and the instrument 24comprises two photomultipliers 26, 28 and respective amplifiers 30, 32.Further, provided in the rotary moving device 18 are a moving motor 34for moving the detection unit 2 back and forth by moving the instrument24 back and forth, and a rotary motor 36 for rotating the detection unit2 by rotating the instrument 24.

The using direction of the radiation detector of the embodiment will bedescribed by referring to an examination of coronary artery lesion as anexample. In this case, radiopharmaceuticals which accumulate in theplaque or thrombus inside the coronary arteries are administered to apatient beforehand.

-   {circle around (1)} First, a guide wire is inserted from an inguinal    region into a blood vessel and the guide wire is moved further into    the coronary artery. Then, guide wire 40 is inserted into a hole 38    provided in the lightproof cover 16 of the detection unit 2 (FIG. 2)    and the detection unit 2 is inserted into the vicinity of the tip    area of the coronary artery along the guide wire 40.-   {circle around (2)} The position of the scintillator 4 is checked by    the X-ray opaque substance 8 mounted onto the top end of the    scintillator 4. The X-ray opaque substance 8 produces a positive    image by radiography performed on the coronary artery. Also, the    action of the rotary moving device 18 is controlled by the computer    22 so that the position of the scintillator 4 can be identified by    the data of the computer 22.-   {circle around (3)} Emission of light is caused when the radiation    emitted from the blood vessel lesion. The light is transmitted to    the optical fiber aggregation 10 connected to the scintillator 4.    The optical fiber aggregation 10 is separated into two optical fiber    branches 12, 14 so that the light is equally divided into two to be    transmitted to the photomultipliers 26, 28. Each light is converted    into electric signals in the photomultipliers 26, 28 and amplified    to be transmitted to the controller 20.-   {circle around (4)} A counter circuit is enclosed inside the    controller 20. The signals from the two photomultipliers 26, 28    enter the counter circuit as pulse for obtaining coincidence. By    narrowing the time width of the pulse, the accidental coincidence    such as background, transmission background and the like can be    eliminated so as to count only the signals form the target radiation    as much as possible. The count rate is transmitted to the computer    22.-   {circle around (5)} The computer 22 displays the count rate based on    the measurements by time and positions and on the directivity of the    radiation on the screen while storing and diagnosing the values.    Then, the description of the lesion is recognized according to the    radiation accumulated area inside the coronary artery, the degree of    the accumulation and the property of the used radiopharmaceutical.    Also, the computer 22 together with the rotary moving device 18    activates the motors 34, 36 for controlling the rotation and the    movement of the scintillator 4.

The radiation detector of the embodiment exhibits the following effects.The radiopharmaceuticals administered beforehand accumulate in thearteriosclerosis lesion area (plaque or thrombus) inside the bloodvessel. The scintillator inserted inside the blood vessel emits lightwhen detecting the radiation emitted from the accumulation. The light istransmitted to the optical fiber in which a number of fibers are bundledup in one to be connected to the scintillator. The optical fiber isdivided into two on the midway so that the light is equally divided intotwo to be transmitted to the photomultipliers. Each light signal isconverted to electric signal (pulse) in the two photomultipliers and, atthe same time, the electric signals are transmitted to the controller.The controller strictly obtains the coincidence and counts only thesignals by the light emitted from the scintillator. At this time,accidental coincidence is avoided by narrowing the time width of thepulse for suppressing the background to minimum. Thereby, it becomespossible to identify the target radiation and detect the smallaccumulation of the radiation in the lesion area. Also, the rotarymoving device can be rotated and moved at a constant speed inside theblood vessel so that it is effective for continuous search for thelesion areas and for identifying the position. The counted values aredisplayed by time and positions on the computer and the data can beanalyzed.

The radiation detector of the embodiment is obtained after investigatingeach of the following issues: miniaturization of the scintillator;improvement of the sensitivity and reduction of the background;recognition of the directivity of the radiation entering thescintillator; recognition of the position of the scintillator inside theblood vessel; and the device for rotating and moving the scintillatorback and forth inside the blood vessel. These issues will be describedin the followings.

(1) Miniaturization of Scintillator

Acute coronary syndromes are caused by thrombus formation due to raptureof the plaque inside the coronary artery. In the conventional nuclearmedical method, it has not been possible to detect such small dose ofradiation accumulated in the plaque or thrombus. The main reason forthis may be that the detection unit cannot be provided closely incontact with the lesion area. The embodiment overcomes theabove-described problem by miniaturizing the scintillator to be insertedinside the coronary artery. In other words, the inner diameter of thecoronary artery is about 3.00 mm in the basal area and about 1.5 mm inthe center area in between the periphery. In the radiation detector ofthe embodiment, the size of the scintillator is miniaturized to have thediameter of about 1.00 mm and the length of about 5.00 mm so that thedetection unit can be inserted to the ramification of the coronaryartery.

Further, in order to improve the sensitivity of the scintillator by notleaking the light emission by the incidence of the radiation as much aspossible and also to effectively transmit the light to the opticalfiber, fine convexoconcaves are provided in the peripheral surface ofthe scintillator so that the light is diffusely reflected inside thescintillator. Conventionally, in order to diffusely reflect the lightinside the scintillator in a large size, a method of winding a tapearound the scintillator or a method of applying white coating on thesurface of the scintillator are employed. However, with the methods, thetape or the coating serves as the shield thereby attenuating theincoming radiation. Also, there is a small space generated in betweenthe tape or the coating and the scintillator so that there causes a lossof the diffused reflection inside the space. Therefore, theabove-described methods cannot be employed for the miniaturizedscintillator. In the embodiment, a new method is employed in which fineconvexoconcaves are provided by directly processing the surface of thescintillator. It is preferable to use plastic or cesium iodide for thematerial of the scintillator. They can detect gamma-ray such as^(99m)Tc, ¹¹¹In, ¹²³I and beta-ray such as ⁸⁹Sr, ⁹⁰Y, ¹⁸⁶Re.

(2) Improvement of Sensitivity and Reduction of Background

As described, in the radiation detector, it is inevitable that thesensitivity is deteriorated due to the miniaturization of thescintillator as described. The radiation detector of the embodiment hasthe sensitivity capable of detecting the small dose of radiationaccumulated in the lesion area inside the blood vessel even though thescintillator is miniaturized into a size capable of being inserted intothe coronary artery. In other words, in the embodiment, some hundreds ofextremely thin optical fibers of about 20 μm diameter are bundled up tohave almost the same thickness as that of the diameter of thescintillator to be connected to a scintillator. In order to effectivelytransmit the light of the scintillator to the optical fiber, it ispreferable to connect one scintillator to one optical fiber. In theembodiment, some hundreds of optical fibers are bundled up since it isnecessary to equally divide the light signal into two for performingcoincidence as will be described later. Thus, it is designed toeffectively transmit the light of the scintillator to the bundle made upof some hundreds of optical fibers.

When each optical fiber is viewed from the cross section, it comprises aclad (light reflex) on the outer side and a core (optical light guide)on the inner side. In order for the light to be guided to the end insidethe core, it is necessary that the angle of incidence to the core iswithin a specific value, and the incoming light at an angle over thevalue does not transmit to the end. The embodiment employs the method ofdiffusely reflect (diffused reflex) the light on the surface of thescintillator as a method for not leaking the light inside thescintillator and for effectively guiding the light to the opticalfibers. The advantage of the method is that rays of light at variousangles are generated by the diffused reflection thereby increasing thedose of the light entering the angle of incidence of any core. Otherexample of the method for not leaking the light inside the scintillatorto the outside, there is a method of totally reflecting the light on thesurface of the scintillator. However, with the method, althoughattenuation of the light due to the reflection is small, there is nochange in the angle of incidence. Therefore, the light entering insidethe angle of incidence of the core is limited to some extent.

Further, in the embodiment, in order to reduce the background, a bundleof optical fibers connecting to the scintillator are divided on the wayinto two for guiding the equally divided light signals into twophotomultipliers to obtain coincidence. In other words, the light signalis converted to the electric signal (pulse) and only the timelycoincided pulse is counted by the controller as coincidence. It isimportant in this method to narrow the time width of the pulse as muchas possible for not picking up the background. In the embodiment, thelights inside the scintillator diffusely reflect on the surface to berays of light at various angles so as to be able to enter a number ofoptical fibers. Also, the two bundles of the optical fibers are arrangedto equally divide the light into two so that the time jitter of thelight signals entering the two photomultipliers become equal. Thisenables to narrow the time width of the pulse as much as possible and toobtain the coincidence. Thereby, only the signals by the emission oflight from the scintillator are counted. By reducing the background tothe minimum as described, it enables to decrease the discriminationlevel so that the sensitivity can be further improved.

(3) Recognition of Radiation Directivity entering Scintillator

The radiation detector of the embodiment can recognize the direction ofthe incoming radiation into the scintillator emitted from the lesionarea inside the blood vessel. Therefore, in the embodiment, a part ofthe top end face and the peripheral surface of the scintillator areshielded by a radiopaque substance. Thus, the radiation from inside thebody entering the scintillator is extremely decreased due to theshielded part. Also, the scintillator covered by the radiopaquesubstance can be rotated at a constant speed (for example, 1 rotation/10seconds). The rotation is connected to the computer and the count of theincoming radiation by each rotation angle is recorded in the computer.Thereby the directivity of the incoming radiation can be obtained. Inother words, it can recognize the direction of radiation emitted fromthe lesion area inside the blood vessel. Thereby, the position of theradiation accumulation can be recognized by the vertical and lateralpositional relation when the blood vessel is viewed by a cross section.

(4) Recognition of Scintillator Position inside Blood Vessel

The radiation detector of the embodiment can recognize the position ofthe scintillator inside the blood vessel. For example, it is possible toalways check the position of the scintillator, i.e. how far (some tenmm) from the tip of the coronary artery or how far (some ten mm) fromthe furcation point to the peripheral. Therefore, in the embodiment, anX-ray opaque substance is mounted onto the top end part of thescintillator. After inserting the scintillator into the blood vessel,the X-ray opaque substance produces an active image by radiography byexternal irradiation so that the accurate position of the scintillatorinside the blood vessel can be obtained.

(5) Device for Rotating and Moving Scintillator Back and Forth in BloodVessel

The radiation detector of the embodiment comprises a rotary movingdevice for rotating the detection unit at a constant speed inside theblood vessel and for moving it back and forth at a constant speed. Forexample, the rotary moving device makes the scintillator, the opticalfibers and the two photomultipliers rotate integrally at a constantspeed (for example, 1 rotation/10 seconds) and makes them move at aconstant speed (for example, 2 mm/10 seconds) by the operation of themotor through the computer control. This method enables to continuouslysearch the accumulated area of the radiation inside the blood vessel andis effective for accurately recognizing the positional relation of theradiation accumulated area.

EXAMPLES Example 1

Effects of the cases where the peripheral surface of the scintillatorwas formed to be a specular surface and where it was formed to be adiffused reflex surface (with fine convexoconcaves) were examined. Inorder to effectively investigate the effects of the surface treatment, aplastic scintillator with the diameter of 3 mm and the length of 15 mmwas used. Optical fiber was connected to the basal end face of thescintillator and photomultipliers were connected to the optical fiber.Beta-ray (90Sr—90Y) was used as the radiation source and the radiationsource was moved by a collimator with the diameter of 1 mm made of aradiopaque substance from the side face of the scintillator to the axialdirection. The photomultiplier pulse height maximum value at this timewas measured by a multi-channel analyzer for measuring the channel ofthe maximum wave. The results of the measurement are shown in FIG. 5 toFIG. 7. The spectral diagrams A to J in FIG. 5 and FIG. 6 show the pulseheight spectrum before energy calibration, where the horizontal axisrepresents the channel showing the energy against the wave value and thevertical axis represents the counting value (cps). In this case, thevertical axis is a logarithmic scale, where the lowest scale is 1, thesecond lowest is 10, the third lowest is 100, the fourth lowest is 1000,the fifth lowest is 10000, the sixth lowest is 100000, and the top scale(upper end of the horizontal axis) is 1000000. The horizontal axis ofthe spectral diagrams A to J is a regular scale (linear scale), wherethe scale in the left end (left end of the vertical axis) is 0 and thescale in the right end (right end of the vertical axis) is 1024. FIG. 7is a graph showing the energy for the wave value.

TABLE 1 Scintillator Surface: Specular Surface Radiation source MaxChannel showing Max Spectral Position (mm) Energy for Wave Value diagram1.5 516 A 4.5 548 B 7.5 560 C 10.5 569 D 13.5 570 E

TABLE 2 Scintillator Surface: Diffused Reflex Surface Radiation sourceMax Channel showing Max Spectral Position (mm) Energy for Wave Valuediagram 1.5 663 F 4.5 669 G 7.5 686 H 10.5 686 I 13.5 690 J

From the results above, it has been verified that the scintillator withthe diffused reflex surface can detect the higher wave than the one withthe specular surface. This indicates the following: the detectionefficiency is improved since the detection count is an integral value ofthe spectral characteristic; the counting value is improved since thedifference of the level (wave value difference) between the electricbackground increases due to an increase of the wave value so that thecount cut by the discriminator becomes less. In other words, it has beenverified that the emitted light is effectively transmitted to thephotomultipliers.

Example 2

A sensitivity test was performed on the radiation detector shown in FIG.1 to FIG. 3. In this case, the scintillator was made of plastic with thediameter of 1.0 mm and the length of 5.0 mm. The optical fiberaggregation was prepared by bundling up some tens of optical fibers withthe diameter of 40 μm to be in the diameter of 0.8 mm and the length of2000 mm. The scintillator and the optical fibers were not covered by alightproof cover so that the test was carried out in a dark field. Thetest results performed on ¹¹¹In as gamma-ray nuclide and ⁸⁹Sr asbeta-ray nuclide are as follows.

1. Detection Efficiency, Detection Limit

After dropping 3.0 μl radiation source into a dent with the diameter of2.0 mm and the depth of 1.3 mm formed in an acryl plate, the dent wassealed and the scintillator was set to be in contact with the radiationsource sealed area for carrying out the measurement. A set ofmeasurement for 10 seconds was repeated for 10 times and the average wascalculated for obtaining the value per second. The results are shown inTABLE 3.

TABLE 3 ¹¹¹In ⁸⁹Sr Background Counting value (cps) 2.3 0.4 Radiationsource Counting value (cps) 36.6 1081.1 Radiation source Radiation Value(KBq) 203.7 85.8 Detection Efficiency (%) 0.018 1.260 Detection Limit(Bq) 14038 1152. Verification of Detection Property

The scintillator was placed on a plate to be in contact with the edge ofthe radiation source (85.8 Kbq/3 μl) and the plate was moved by every0.25 mm along the axis of the scintillator. 1 point was measured for 10seconds and the average measured counts per second was obtained. Onlythe result of the measurement performed on ⁸⁹Sr is shown in FIG. 8.

3. Detection Scanning Test using Simulated Blood Vessel

A catheter (inner diameter of 1.57 mm, the thickness of 0.255 mm) wasused as a simulated blood vessel and four plates with different dose ofradiation were continuously placed on the external surface of thecatheter. The radiation doses were set to be 16.9 KBq, 4.2 KBq, 84.5 KBqand 8.5 KBq and the volume was 3 μl for all. After inserting thescintillator inside the catheter, the detecting property was measured.In this case, 1 point was measured for 10 seconds and the average valueper second was obtained. Only the result of the measurement performed on⁸⁹Sr is shown in FIG. 9.

4. Linearity of Radiation Dose and Counting Value

The linearity of the counting value against the concentration of ⁸⁹Srused on the above-described detection scanning test using the simulatedblood vessel was examined. The results are shown in FIG. 10.

From the results of the above-described sensitivity tests, it has beenclarified that the radiation detector of the present invention can makethe background be the minimum and exhibits an excellent sensitivity forthe gamma-ray and beta-ray. Especially, it exhibited an excellentsensitivity for beta-ray. Also, it has been concluded that it ispossible to detect the radiation accumulation of gamma-ray since thecomparison against the background was sufficiently large. The tests onthe detecting property and the detection scanning using the simulatedblood vessel were further performed on ⁸⁹Sr. There were clear peaks forthe radiation source positions in each test so that it has been verifiedthat a small radiation accumulation such as the case of lesion insidethe blood vessels can be detected. Also, there was almost linearrelation between the radiation dose of the radiation source and thecounting value so that the credibility of the measured value wasverified.

INDUSTRIAL APPLICABILITY

As described, with the radiation detector of the present invention, itis possible to detect the radiation leakage from the tubules andradioactive substances accumulated in tissue inside a body by insertinga detection unit into the tubules or the blood vessels.

Specifically, the radiation detector of the present invention exhibits,for example, the following effects. Acute coronary syndromes (referredto as ACS in the followings) are especially serious diseases among heartdiseases. Conventionally, it has been considered that ACS is caused bysevere stenosis of coronary artery due to arteriosclerosis. However,recently, it has been clarified that ACS is caused without a significantstenosis. Lately, it is believed that ACS is caused by thrombusformation due to rapture of the plaque in the endothelium of thecoronary artery and it is said to have a stronger relation with theproperties of the plaque and the blood vessel endothelium covering theplaque than the degree of the stenosis of the coronary artery.Therefore, in order to predict possible ACS, it is most important todetect the plaque which is to be easily ruptured inside the coronaryartery.

Recently, various detection devices have been tried to predict possibleACS. There is a report that the presence of the plaque can be recognizedby tomogram of the coronary artery through the intravascular ultrasound. There is also a report that the presence of the plaque in theendothelium can be speculated by an eye observation of the inside thecoronary artery through the intravascular endoscope. However, with theseexaminations, it is believed to be extremely difficult to predict thepossible ACS. Both lack the information regarding the properties of theblood vessel endothelium and the plaque.

Originally, nuclear medicine method is an excellent method forrecognizing the properties of the functions and tissue of the livingbody, since it is an examination in which the chemical substancesreflecting the function and property are labeled by radiation and theaccumulation and excretion are traced. However, as described, it hasbeen impossible to detect a small lesion such as the one inside thecoronary artery with the conventional nuclear medicine method.

On the contrary, with the radiation detector of the present invention,it is possible to detect the radiation accumulated in the plaque andthrombus by inserting the detection unit into the inside the coronaryartery. Also, with the present invention, it is possible to identify thevulnerable plaque by administering a chemical substance for showing theproperties of the blood vessel endothelium and the plaque as theradiopharmaceutical. It may be extremely a large contribution to medicaltechnology when the possible ACS can be predicted by the presentinvention.

1. A radiation detector for detecting a radioactive substance present ina tubule, or in the vicinity of said tubule comprising a detection unithaving a bar-type scintillator which emits light by an incidence ofradiation thereby transmitting the light from said scintillator throughan optical fiber, wherein said detection unit is formed in a sizecapable of being inserted into the tubule while a roughened surface isprovided on the peripheral surface of said scintillator, the diameter ofsaid scintillator is set to be substantially 1.5 mm or less, saidoptical fiber for transmitting the light from said scintillator is anoptical fiber aggregation which is obtained by bundling up thin opticalfibers to have substantially the same diameter as that of saidscintillator, said aggregation is divided into two optical fiberbranches thereby dividing the light equally for transmitting tophotomultipliers, said photomultipliers receive said divided lights forconverting and amplifying each of said light into electric signals, anda counter circuit of a controller receives and counts said electricsignals as pulse for obtaining coincidence.
 2. A radiation detector fordetecting a radioactive substance present in tissue in a body system,comprising a detection unit having a bar-type scintillator which emitslight by an incidence of radiation thereby transmitting the light fromthe said scintillator through an optical fiber, wherein said detectionunit is formed in a size capable of being inserted into a blood vesselwhile a roughened surface is provided on the peripheral surface of saidscintillator, the diameter of said scintillator is set to besubstantially 1.5 mm or less, said optical fiber for transmitting thelight from said scintillator is an optical fiber aggregation which isobtained by bundling up thin optical fibers to have substantially thesame diameter as that of said scintillator, said aggregation is dividedinto two optical fiber branches thereby dividing the light equally fortransmitting to photomultipliers, said photomultipliers receive saiddivided lights for converting and amplifying each of said light intoelectric signals, wherein a counter circuit of a controller receives andcounts said electric signals as pulse for obtaining coincidence.
 3. Theradiation detector according to claim 1 or claim 2, wherein a part ofthe top end face and the peripheral surface of said scintillator arecovered by a radiopaque substance for determining the position of thescintillator using radiography.
 4. The radiation detector according toclaim 1 or claim 2, further comprising a rotary moving device forrotating and moving said detection unit back and forth in a tubule orinside a blood vessel.